As a semiconductor device is more highly integrated, the number of metal lines increases. Meanwhile, a pitch of the metal line decreases gradually. As the pitch of the metal line decreases, a resistance of the metal line increases. Also, a parasitic capacitance between an insulating interlayer for the metal line and the corresponding metal line is generated, thereby deteriorating the characteristics of the semiconductor device. As a result, it is necessary to provide a low dielectric insulating interlayer suitable for the high-integration semiconductor device. Recently, a Boron-Phosphorus Silicate Glass (hereinafter, referred to as “BPSG”) layer and a Fluorine Silicate Glass (hereinafter, referred to as “FSG”) layer have been developed for use a low dielectric insulating interlayer. Both of these recently developed layer are applied in a wide range of applications.
As shown in FIG. 1, a known semiconductor device includes a semiconductor substrate 1 having lower components. In this state, an insulating interlayer 2 of a BPSG layer or an FSG layer is deposited on the semiconductor substrate 1. Then, a contact hole H is formed in the insulating interlayer 2, and a contact plug 6 is formed therein for an electric contact between the lower components and a metal line 5. Also, a barrier metal layer 7 is additionally formed inside the contact hole H to improve the electric contact of the contact plug 6 and a reflection prevention layer 4 is formed on the insulating interlayer 2 for formation of the contact hole H.
In the drawings, for convenience, the reflection prevention layer 4 is depicted in the completed semiconductor device. However, in fact, after the reflection prevention layer 4 is used to prevent the diffused reflection of pattern light (for example, UV rays) when forming the contact hole H by pattering a photoresist pattern, the reflection prevention layer 4 is completely removed in the semiconductor device by the following polishing process.
In the known semiconductor device, if the insulating interlayer 2 of the BPSG layer or the FSG layer is exposed to the atmosphere without the additional process, an amorphous material layer is unnecessarily formed in the surface of the insulating interlayer 2. To prevent this problem, as shown in the drawings, a protective oxide layer, for example, a SiH4-oxide layer 3 is additionally formed on the insulating interlayer 2. By forming the SiH4-oxide layer 3, it is possible to prevent the amorphous material layer from generating in the surface of the insulating interlayer 2.
The SiH4-oxide layer has the most stable chemical structure among oxide layers formed by plasma, whereby it is possible to effectively prevent the formation of the amorphous material layer. However, because the SiH4-oxide layer contains hydrogen, the hydrogen goes out of an interface during the fabrication process.
In this state, as shown in the drawings, if the reflection prevention layer 4 for forming the contact hole is formed on the corresponding SiH4-oxide layer at an acidity between (ph)3- and (ph)4, as shown in FIG. 2, the hydrogen 3a is rapidly transferred to the reflection prevention layer 4 and is combined with the oxygen 4b of the reflection prevention layer 4, thereby generating the hydroxide group (4a:OH—). As a result, the acidity (ph) of the reflection prevention layer 4 is lowered so that the reflection function of the reflection prevention layer 4 deteriorates.
Under the deterioration in the function of the reflection prevention layer, in case of performing the photoresist pattern process by using the corresponding reflection prevention layer and the process of forming the contact hole by using the photoresist pattern, the completed contact hole H is formed in a barrel type or shape due to a bowing phenomenon generated by the diffused reflection of the reflection prevention layer 4. In this state, if the barrier metal layer 7 and the contact plug 6 are formed without the additional process, it is impossible to stably fill the inside of the contact hole with the barrier metal layer 7 and the contact plug 6. As a result, the metal line 5 may not be stably and electrically connected with the semiconductor substrate 1, thereby deteriorating the quality of the completed semiconductor device.